The present invention is related to the following GE application 11/809,122, filed on May 31, 2007, respectively.
The invention relates generally to a new topology for a 7-level wye-connected H-bridge converter that provides redundancy for continued operation when one bridge phase has failed and more particularly to a topology that includes multiple semiconductor H-bridges and a three-phase semiconductor mid-bridge. Individual bridges of the converter may be operated at different dc-bus voltages to maximize power output. The converter may employ synchronous gating signals for the semiconductor devices of the bridges, including a zero-current notch waveform for minimizing harmonic distortion of the output waveform and increasing power output of the converter.
High-speed, high-power electric motors that operate at variable speed are increasingly required in a range of industrial, mining and drilling activities. Further, the activities often require a high-degree of reliability. In operations such as crude oil pumping from remote global locations where access to pumping stations is difficult and time-consuming, reliability of motor operation is necessary to prevent dangerous, costly and extended outages. Simple, sturdy and reliable power converters are requisites for such high-speed, high-power motor operations. It is well known that providing multiple individual components, such as series or parallel semiconductor switches, may increase the likelihood that any one individual component switch may randomly fail. Added elements such as snubber circuits for semiconductor switches, further increases the number of components that can fail. It is desirable to arrange the power converter in a simple configuration, with as low a part component count as is possible. However, individual components such as the semiconductor switches for the power converted must be operated with satisfactory margin to thermal and other functional limits to prevent failures in the simplified configuration.
A simplified three-phase, wye-connected H-bridge converter configuration is illustrated in FIG. 1. Each phase of the converter includes a power source/sink 20 with a dc power shaping circuit, represented by capacitor 30. The power source/sink 20 and dc power shaping circuit, represented by capacitor 30, establish a dc-bus voltage input to the semiconductor switches 40 of the bridge. Insulated-gate bipolar transistor (IGBTs) semiconductor switches 40 with built-in diodes 45 may form each leg of the H-bridges 50, for example, but other power semiconductor switches such as integrated-gate commutated thyristors (IGCTs) or metal-oxide semiconductor field-effect transistors (MOSFETs) could be used instead. The type of power semiconductor switch is not important to the analysis. Each H-bridge includes two legs, an output leg 60 and a neutral leg 65. Each phase output, phase A 70, phase B 75 and phase C 80, is connected to the midpoint 85 of the respective output bridge leg 60. Each neutral connection to wye-point 90 is tied to the midpoint 95 of the respective neutral output leg 65. A gating control 115 providing gating signals 116, 117, 118 for switching the semiconductor devices 40 of the H-bridges 50 may also be provided.
While the above-described three-phase, wye-connected H-bridge converter provides simplicity, should failure occur in one of the phase H-bridges, normal operation of large high-speed electric motors (HSEMs) loads will be interrupted.